Corona free coupling assembly for coaxial cables

ABSTRACT

A corona free coupling assembly for connecting high voltage coaxial cables comprising a body of elastomeric insulating material having an elongated bore open at opposite ends for receiving end portions of said cable. A tubular inner shield means is embedded in said body in coaxial alignment in said bore and spaced from opposite ends thereof; a tubular connector sleeve is insertable into the bore of the filler body within the inner shield means for connecting the conductors of said cables in endto-end relation; integrally formed contact means projecting inwardly of the bore of said inner shield means is provided for making electrical contact between the inner shield means and said connector sleeve when the latter is inserted within the former; conductive outer shield means is provided on the outer surface of an insulating housing receiving the elastomeric filler body for connecting the outer shielding systems of the cables together in coaxial relation with said inner shield means.

United States Patent Misare June 27, 1972 44 I2d' 4o 28 42 26 'lililililii s s K a a Primary Examiner-Laramie E. Askin Attorney-Mason, Kolehmainen, Rathbum & Wyss [57] ABSTRACT A corona free coupling assembly for connecting high voltage coaxial cables comprising a body of elastomeric insulating material having an elongated bore open at opposite ends for receiving end portions of said cable. A tubular inner shield means is embedded in said body in coaxial alignment in said bore and spaced from opposite ends thereof; a tubular connector sleeve is insertable into the bore of the filler body within the inner shield means for connecting the conductors of said cables in end-to-end relation; integrally formed contact means projecting inwardly of the bore of said inner shield means is provided for making electrical contact between the inner shield means and said connector sleeve when the latter is inserted within the former; conductive outer shield means is provided on the outer surface of an insulating housing receiving the elastomeric filler body for connecting the outer shielding systems of the cables together in coaxial relation with said inner shield means.

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]..-\"\/E,N"1OR.' DONALD O. MISARE BY CORONA FREE COUPLING ASSEMBLY FOR COAXIAL CABLES The present invention is directed towards a new and improved corona free coupling assembly used for connecting or splicing together high voltage coaxial cables of the kind generally used for underground power distribution systems.

The present invention is an improvement over the cable splice shown in FIG. 8 of U.S. Pat. No. 3,290,428 and is especially designed to eliminate corona discharge, which is often a problem in many prior'art coupling assemblies used for high voltage coaxial cables, and the like.

Corona problems develop whenever sufficient electrical voltage difference is present between spaced conductors, separated by air spacing or air pockets. Corona, in addition to wasting power, is deleterious to many insulating materials and often causes physical deterioration and rapid chemical decomposition thereof. In addition, corona envelopes cause a radio interference and noise which is objectionable;

' The present invention has for an object the provision of a new and improved corona free coupling assembly for use in connecting ors licing together high voltage coaxial cables of the type generally used'in high voltage underground power distribution systems and'the like.

Another object of the present invention is to provide a new and improved corona free coupling assembly of the character described which is low in cost, easy to assemble and install, and which is extremely reliable in operation over along period of useful life.

Another object of the present invention is to provide a new and improved corona free coupling assembly of the .type described in which a symmetrical pattern voltage stress gradient is obtained within the insulating material of the coupling assembly between the inner and outer shield systems.

Another object of the invention is to provide a new and improved coupling assembly of the character described wherein high voltage electrical stress is not applied directly across air spaced conductors. v 1

'Another' object of the present invention is to provide a new and improved coupling assembly of the character described employing an elastomeric filler having an inner conducting shield means' embedded therein for establishing an inner shielding system within the assembly around the coupled together connectors, which inner shield system -is symmetrically arranged with respect to a concentric outer shield system around the outsidesurface of the coupling assembly connecting together the outer shield systems of the coaxial cables.

Another object of the present invention is to provide a new and improved coupling assembly of the character described employing a housing formed of rigid insulating material such as wet process porcelain and having a conductive glaze formed on the outer surface of the housing providing an outer shield means for connecting the outer shield systems of the cables which are spliced together.

Briefly, the foregoing and other objects and advantages of the present invention are accomplished in a new and improved corona free coupling assembly for connecting high voltage coaxial cables comprising a filler body of elastomeric insulating material having an elongated bore open at opposite ends for receiving the end portions of said cables. Tubular conductive inner shield means of elastomeric material is embedded in the body in coaxial alignment in the bore and spaced from opposite ends thereof. A tubular connector sleeve is inserted into the bore within inner shield means for connecting the central connectors of the cables in end-to-end relation. integrally formed deflectable contact means are provided to extend inwardly of the bore of the inner shield means for making electrical contact between the inner shield means and the connecting sleeve when the latter is inserted within the bore. The filler is mounted in the bore of a hollow, elongated insulating housing formed of porcelain and the like, and a conductive outer shield means comprising a conductive glaze formed on the outside surface of the housing is provided for connecting the outer shield systems of the spliced together cables.

For a better understanding of the invention, reference should be had to the following detailed description taken in conjunction with the drawings, in which:

FIG. 1 is a side elevational view of a new and improved coupling assembly for coaxial cables constructed in accordance with the features of the present invention;

FIG. 2 is a transverse cross section of the coupling assembly taken substantially along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken substantially along line 3-3 of FIG. 1; and

FIG. 4 is a longitudinal sectional view through the coupling assembly showing the internal components thereof.

Referring now, more particularly, to the drawings, therein is illustrated a new and improved corona free coupling assembly generally referred to by the reference numeral 10. The coupling assembly 10 is especially adapted for connecting together or splicing the ends of a pair of high voltage coaxial cables 12 and 14 of the type commonly used in underground power distribution systems.

The cable 12 includes a central conductor 120 comprising a plurality of individual wires spirally wound and surrounded by a concentric insulating jacket 12b preferably formed of molded polyethylene material which is extruded onto the inner conductor 12a. The insulating jacket 12!; is surrounded by a conductive outer shielding system which includes a wrapping of conductive tape 12c and a plurality of neutral wires 12d wrapped in a spiral pattern around the tape. Similarly, the cable 14 includes a central conductor 14a formed of a plurality of spirally wound individual wires surrounded by a concentric insulating jacket 14b, an outer shielding system comprising a. wrapping conductive tape 14c with a plurality of individual neutral wires 14d spirally wrapped around the tape.

Inv preparing the end portions of the cables 12 and 14 for splicing together in the coupling assembly 10, the neutral wires 12d and 14d, respectively, are stripped back or unraveled from the end of the. cable for a predetermined distance, and one of the neutral wires is wound around the cable body in a plurality of concentric adjacent retaining rings 12c and Me, respectively, to prevent further unraveling of the neutral wires from the cable body. The neutral wires are then woven into cables 12d and 14d, respectively, and are connected together externally of the coupling assembly with a compression connector fitting 16. As best shown in FIGS. 1

. and 3, some of the neutral wires, for example the wires l4d' are braided into a separate grounding cable, which cable is secured mechanically and electrically to a ground lug 24a on an end cap member 24, as will be described hereinafter.

in accordance with the present invention, the coupling assembly 10 includes an elongated, tubular body 20 formed of rigid, strong insulating material, such as wet process porcelain, and the body includes an elongated, cylindrical axial bore 22 of substantially uniform diameter throughout its length. The

opposite ends of the porcelain housing are formed with a pair of annular ridges or end flanges 20a in order to mount a pair of metal cap-like terminal members 24. Immediately inwardly of the end flanges 24, the outer surface of the porcelain body 20 is fonned with grooved annular recesses 20b each having a frustoconical surface 200 sloping radially outwardly of the iongitudinal axis of the coupling assembly and inwardly toward the center of the body away from the respective end flanges so that the dielectric insulation around the cable gradually increases towards a maximum from the point at which the outer shield system (tape coverings 12c and 14c) are stripped back.

In accordance with the present invention, the outer surface of the porcelain insulator body 20 is covered with an electrically conductive glaze 26 which provides a continuous symmetrical outer shielding system for the coupling assembly and the outer shield systems of the spliced together cables 12 and 14. The metallic end caps 24 are in direct contact around the conductive glaze 26 formed on the outer surfaces of the housing end ridges 20a and each end cap 24 includes one or more radially outwardly extending slotted lugs 240 (FIG. 3) so that a braided conductor formed by the outer neutral wires 12d or 14d of the cables can be grounded or connected to at least one end cap (for example, the conductor Md). The end caps 24 and glaze 26 are thus maintained at the same potential as the outer shield systems of the cables 12 and M, and the braided cables 12d and 14d are also held in direct contact against the conductive glaze by rings of tape 28 at several longitudinally spaced locations on the porcelain body 20. From the foregoing, it will be seen that a continuous outer shielding system at common electrical potential is obtained by the connection of the braided outer neutral wires 12d" or 14d" with the lugs 24a on one or more end caps 24. The end caps are in turn electrically connected to the outer shielding conductive glaze 26 on the outer surface porcelain insulator body 20. The braided neutral cables 12d and 14d are directly connected together by the compression connector fitting 16 externally of the coupling assembly.

In accordance with the present invention, a tubular elastomeric insulating filler 30 is inserted into the elongated cylindrical bore 22 of the porcelain housing to increase the insulation around the coupled together central conductors 12a and 14a of the cable in the region around the connection. The elastomeric filler includes an elongated bore including opposite end portions 30a having a nominal diameter substantially equal to the diameter of the insulating jackets 12b and 14b of the cables. An inner, tubular shield 32, formed of conductive elastomeric material is embedded within the bore of the insulating tubular filler 30 and is spaced between the opposite bore sections 30a. The inner shield member 32 has a bore 320 slightly larger in diameter than the nominal outer diameter of the cable insulating jackets 12b and 14b. The central conductors 12a and 14a of the respective cables are electrically and mechanically connected together by a tubular compression connector sleeve 36 which is deformed radially inwardly on the cable conductors with a compression crimping tool to secure the conductors tightly together in end-toend relation within the sleeve.

The sleeve 36 is Slightly smaller in outer diameter than the nominal diameter of the cable insulating jackets 12b and 14b so that after the sleeve is secured to splice the cables together in end-to-end relation, both the cables and sleeve can be easily passed through the bore portions 300 of the filler 30 with little difficulty until the sleeve is centered longitudinally of the filler inside the inner shield tube 32.

In order to make electrical contact between the sleeve 36 after it is centered longitudinally of the filler 30 within the bore of the conductive elastomeric inner shield tube 32, a plurality of longitudinally extending, radially spaced and inwardly directed integral ribs 32b are provided in the inner shield tube (FIG. 4), and the inner edge portions of the ribs are adapted to directly contact the outer surface of the sleeve 36 when it is centered in position, thereby establishing electrical contact between the cables 12 and 14, connector sleeve 36, and the inner shield tube 32. The ribs 32b are shaped as arcuate sectors (FIG. 4) to permit easy insertion of the spliced together cables and sleeve from either end of the coupling assembly 10. The ribs 32b are deflectable and project inwardly far enough to automatically establish electrical contact with the connector sleeve 36 when it is inserted and centered within the inner shield 32.

It will thus be seen that even though the chamber 34 may be filled with air, there is no electrical stress or voltage gradient imposed across the air gap because of the direct electrical contact between the contact ribs 32a of the inner shield tube 32 and the connector sleeve 36 which couples the conductors 12a and 14a together. The inner shield tube 32 is in centered, symmetrical, coaxial relation within the outer shielding system formed by the conductive glaze 26 on the outer surface of the porcelain housing 20, and, accordingly, there is no voltage gradient or electrical stress between the inner and outer shield systems in the coupling that is applied across an air space or air gap.

In order to exert compression against the ends of the elastomeric insulating filler 30, and thereby exclude substantially any air from between the interfacing surfaces of the filler and the bore 22 of the porcelain housing 20, and also to exert inward compression of the filler bore surfaces 30a against the cable insulating jacket 12b and 14b, a pair of compression springs 40 are mounted at opposite ends of the housing 20 in coaxially centered relation around the longitudinal axes of the cables 12 and 14. The springs 40 are adapted to exert compressive end thrust on opposite ends of the tiller 30 to thereby initially expel any air from between the contacting insulating surfaces as described and thereafter to maintain a substantially air free interfacial engagement between the surfaces. To permit easy sliding movement of the connected together cables along the bore of the elastomeric filler 30, the compression springs 40 are maintained in an initially restrained or compressed condition so that no end force is exerted by the springs on the tiller body 30 during initial insertion and centering of the cables and sleeve 36 in the filler. For this purpose an annular washer or ringlike retainer 42 is mounted adjacent the inner end of the springs to bear against the adjacent surface of the elastomeric filler body 30. The annular retainers 42 are provided with a pair of longitudinally extending legs 44 which extend parallel of the cables and project outwardly through slots 240 (FIG. 3) provided in the annular end walls of the metallic caplike terminal members 24. The springs 40 are maintained in a compressed condition by means of removable key members 46 (FIG. 3) formed of wire and having loops at their outer ends. Each key includes a leg projecting through a slot adjacent the outer end of a spring restraining leg 44 as shown in FIG. 3, and after the spliced together cables have been inserted and centered in the coupling assembly I0, the keys 46 are extracted manually by pulling the looped outer ends in a radially outward direction, as indicated by the arrows "A" (FIG. 3) to release the legs 44 and the springs 40 to compress opposite ends of the filler 30. In order to establish when the sleeve 36 is centered longitudinally of the inner shield 32 before releasing the springs 40, a marker tape 48 (FIGS. 1 and 4) is applied around one of the cables at a prescribed distance from the end, and when the tape is positioned adjacent an end fitting 24, the desired amount of insertion of the sleeve and cables is obtained.

The metallic end cap members 24 are formed with annular side walls which fit over the end ridges 20a on the porcelain housing. The side walls of the members are turned inwardly at their free edges, preferably in a metal spinning operation, to bear against the inner radial faces of the ridges 20a and securely hold the cap members in place on the housing 20.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A corona free coupling structure comprising a pair of high voltage coaxial cables with outer shielding means, a coupling assembly including a tubular housing of rigid insulating material; a filler body of elastomeric insulating material inserted into said housing and having an elongated bore open at opposite ends receiving the end portions of said cables; tubular conductive inner shield means embedded in said body in coaxial alignment in said bore and spaced from said opposite ends thereof; a tubular connector sleeve inserted into said bore within said shield means connecting the central conductors of said cables in end-to-end relation; contact means making electrical contact between said inner shield means and said connector sleeve; and outer conductive shield means on said housing connecting the outer shielding means of said connected cables.

2. The coupling structure of claim 1 wherein said housing is formed of porcelain and said outer conductive shield means comprises a conductive glaze applied on the outer surface of said housing.

3. The coupling structure of claim 2 including means exerting resilient end thrust on at least one end of said filler body when inserted in said housing.

end portions in contact against said sleeve.

5. The coupling structure of claim 4 wherein said projections are arcuately shaped for permitting insertion of said 5 sleeve into said filler body from either end. 

1. A corona free coupling structure comprising a pair of high voltage coaxial cables with outer shielding means, a coupling assembly including a tubular housing of rigid insulating material; a filler body of elastomeric insulating material inserted into said housing and having an elongated bore open at opposite ends receiving the end portions of said cables; tubular conductive inner shield means embedded in said body in coaxial alignment in said bore and spaced from said opposite ends thereof; a tubular connector sleeve inserted into said bore within said shield means connecting the central conductors of said cables in end-to-end relation; contact means making electrical contact between said inner shield means and said connector sleeve; and outer conductive shield means on said housing connecting the outer shielding means of said connected cables.
 2. The coupling structure of claim 1 wherein said housing is formed of porcelain and said outer conductive shield means comprises a conductive glaze applied on the outer surface of said housing.
 3. The coupling structure of claim 2 including means exerting resilient end thrust on at least one end of said filler body when inserted in said housing.
 4. The coupling structure of claim 2 wherein said inner shield means has an internal diameter greater than the outer diameter of said sleeve defining an annular space around said connector sleeve and cables within said body, said contact means comprising a plurality of circumferentially spaced, radially inwardly directed projections having deflectable inner end portions in contact against said sleeve.
 5. The coupling structure of claim 4 wherein said projections are arcuately shaped for permitting insertion of said sleeve into said filler body from either end. 